Use of nanoscale particles for creating scratch-resistant protective layers on semiconductor chips

ABSTRACT

Inorganic-based nanoparticles, such as nanoparticles based on silicon dioxide, are used in order to produce protective layers for semiconductor chips having scratch-resistant properties. The nanoparticles are preferably processed to form a sol, which is applied onto the semiconductor chips to be coated and subsequently converted by sintering into the protective layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/DE2005/000476, filed on Mar. 16, 2005, entitled “Use of NanoscaleParticles for Creating Scratch-Resistant Protective Layers onSemiconductor Chips,” which claims priority under 35 U.S.C. §119 toApplication No. DE 102004015403.1 filed on Mar. 26, 2004, entitled “Useof Nanoscale Particles for Creating Scratch-Resistant Protective Layerson Semiconductor Chips,” the entire contents of which are herebyincorporated by reference.

FIELD OF THE INVENTION

The invention relates to providing protective layers for semiconductorchips.

BACKGROUND

Protective layers based on nanoscale particles are known from thefollowing publication: “Thermische Aufbringung neuartigerKorrosionsschutzschichten für Leichtmetalle auf der Basis oxidischerNanopartikel” [Thermal application of novel corrosion protection layersfor light metals based on oxidic nanoparticles], H.-Q. Nguyen, W.Fürbeth, M Schütze, Karl—Winnacker-Institut of DECHEMA e. V, Frankfurtam Main, the disclosure of which is incorporated herein by reference inits entirety. Protective layers based on polymeric or particulate solsare disclosed, which can be applied onto a workpiece surface as a sol bysimple mechanical coating techniques such as dip and spin coating. Theresulting protective layers are purely inorganic, transparent andcurable or sinterable even at a low temperature and have a highmicrohardness in addition to a very good corrosion protection effect.

Protective layers based on nanoscale particles are already applied ontoglass and plastic surfaces, in order to provide-them with a water- anddirt-repellent surface (i.e., a lotus effect).

The use of protective layers based on nanoscale particles for producingscratch-resistant varnishes for automobile paint is also being studied.

In recent years, the need has likewise arisen in the semiconductorindustry to protect unencapsulated semiconductor chips particularlyagainst mechanical damage such as scratches in a simple and reliableway.

There are two reasons for this need. On the one hand, unencapsulatedsemiconductor chips are handled in a semiconductor assembly as aninherent result of the process. On the other hand, in particular packagetypes, so-called “bare dice” or unencapsulated semiconductor chips areused which remain unencapsulated, for example, in order to improve theheat transport out of the semiconductor chip or in order to minimize thespace requirement of the semiconductor component. Both cases entail therisk that the corresponding semiconductor component will become damagedby scratches, particularly as a result of handling.

SUMMARY

The present invention provides a method for producing a protective filmon semiconductor chips, which protects the semiconductor chips againstmechanical damage or scratches.

In accordance with the present invention, nanoscale particles are usedfor producing protective layers, in particular scratch-resistantprotective layers on semiconductor chips. In particular,nanoparticle-based and/or nanocomposite-based coatings, which arepreferably produced using a sol-gel process and applied by simple andconventional methods such as immersion, casting, spraying, printing,rolling, dip coating, spin coating and the like, are suitable forprotecting a semiconductor chip.

The above and still further features and advantages of the presentinvention will become apparent upon consideration of the followingdetailed description of specific embodiments thereof, particularly whentaken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a flowchart outlining a process for forming a protectivelayer in accordance with the invention.

DETAILED DESCRIPTION

Nanoscale particles are formed for producing protective layers inaccordance with the invention, in particular scratch-resistantprotective layers on semiconductor chips. As used herein, the term“nanoscale” in relation to particles refers to particles having sizes ordimensions (e.g., diameters) no greater than about 100 nanometers (nm).In particular, nanoparticle-based and/or nanocomposite-based coatings,which are preferably produced using a sol-gel process and applied bysimple and conventional methods such as immersion, casting, spraying,printing, rolling, dip coating, spin coating and the like, are suitablefor protecting a semiconductor chip.

The use of nanoparticle-based coatings according to the inventionprovides a number of advantages including, without limitation, thatfurther properties can be imparted to the coating by the selection ofsuitable nanoparticles and/or additional doping. In addition toprotecting against scratches, the unencapsulated semiconductor chip canfurther be protected, for example, against light or UV radiation, dirtparticles, moisture and/or uncontrolled electrostatic discharges byselecting appropriate nanoparticles for the coatings in accordance withthe invention.

Sols which contain the nanoparticles either in a particulate orpolymeric form, and which can be applied in a simple way onto thesemiconductor chips to be coated, are preferably used for preparing thescratch-resistant coatings according to the invention. All conventionalmethods for applying a liquid are suitable for applying a sol, such asimmersion, casting, spraying, printing, rolling and, particularly forproducing layers with an accurately defined thickness, dip or spincoating.

Nanoparticles, the synthesis of which can be achieved by a variety ofdifferent conventional methods, are used for particulate sols. Anexample of industrial synthesis is the Aerosil® process, which involvesa continuous flame pyrolysis of silicon tetrachloride (SiCl₄). The SiCl₄is converted into the gas phase and subsequently reacts spontaneouslyand quantitatively inside an oxyhydrogen flame with the intermediaryformed water to form the desired silicon oxide. By varying theconcentration of the reaction partners, the flame temperature and theresidence time of the silica in the combustion space, it is possible toinfluence the particle sizes, the particle distribution, the specificsurface as well as their constitution in wide limits. In a subsequentstep, a suspension or a sol is then produced from the nanoparticles byusing a dispersant.

It is furthermore known that other oxides, such as aluminum oxide ortitanium oxide, alkali metal oxides and/or further metal and/or ceramicmixed oxides can respectively be used as the nanoparticles as analternative or in addition to silicon dioxide in order to impart otherproperties to the protective layer.

Branched silane macromolecules are needed for preparing polymeric sols.These are prepared under acid catalysis starting from silanes. Otheralkoxides can also be used so that it is possible to producemulticomponent nanoparticles and therefore protective layers withdifferent properties.

After the sol has been prepared, it is applied by customary mechanicalmethods for applying liquids as a thin layer onto the semiconductor chipto be coated.

Based on the use of methods such as immersion, casting, spraying,printing or rolling, it is readily possible to use a coating accordingto the present invention in a way which is compatible with massproduction in semiconductor fabrication.

The applied sol layer is then converted into a gel layer, the so-calledgreen layer, by flocculation or aging and/or drying. The green layer issubsequently converted into the scratch-resistant protective layeraccording to the invention by a sintering process, optionally with theaid of sintering additives to reduce the sintering temperature.

These method steps are collated or set forth in a flow chart depicted inFIG. 1. In particular, the steps of FIG. 1 are as follows. Nanoparticlescan be produced from silicon oxide and/or mixed oxide particles (step 1a), and/or by hydrolysis of silanes and/or alkoxides (step 1 b). A solis prepared with such nanoparticles (step 2). The sol is then appliedonto a semiconductor chip (step 3) and then converted to a green layer(step 4). The green layer is then converted to the finished protectivelayer (step 5), for example, via a sintering process.

Possible sintering temperatures for such a process may be about 400degrees Celsius, as is known (e.g., as set forth in above-identifiedpublication of H.-Q. Nguyen et al.). Temperatures of about 400 degreesCelsius are known and usual in semiconductor assembly, for example, ineutectic or soft solder chip assembly processes. For heat-sensitivesemiconductor chips, it is furthermore possible to achieve lowersintering temperatures with efficient reaction rates by using so-calledsintering additives.

The following procedure is adopted in one exemplary embodiment toproduce a protective film, for example from a borosilicate sol, on awafer of semiconductor chips according to the invention.

The silanes are first prehydrolyzed. Triethyl borate is then added. Thisprocedure is necessary in order to compensate for the faster hydrolysisrate of triethyl borate. Because of the high susceptibility of triethylborate to heterogeneous precipitation of a boric acid phase under airhumidity, the borosilicate gel is prepared in a protective chamberflushed with nitrogen. The resulting glass-clear multioxide sol is madeready for coating by storing at room temperature for about 8 hours.

In order to coat the wafer with the sol by spin coating, the sol isfirst applied with a pipette and the wafer is subsequently spun byrotation. The sol layer thickness can in this case be determined byselecting the rotation speed.

The applied sol layer is converted into the green layer by gelling thesol particles or aging the layer with evaporation of the solvent. Thewafer with the green layer is subsequently kept in a drying oven undersynthetic air at approximately 400 degrees Celsius for approximatelyabout 4-10 hours, the green layer becoming condensed to form a vitreouscoat.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof. Accordingly, it is intendedthat the present invention covers the modifications and variations ofthis invention provided they come within the scope of the appendedclaims and their equivalents.

1. A method for coating semiconductor chips with nanoscale particles,comprising: producing nanoparticles comprising at least one of silicondioxide particles, metal particles and ceramic oxide particles;preparing a sol of the nanoparticles; coating semiconductor chips withthe sol; forming a gel layer or green layer from the sol by at least oneof aging and drying the semiconductor chips coated with the sol; andforming a protective layer on the semiconductor chips by sintering thesemiconductor chips coated with the gel layer or green layer.
 2. Themethod of claim 1, wherein sintering additives are added to reduce thesintering temperature required to form the protective layer.
 3. Asemiconductor chip including a protective layer coating at least aportion of the semiconductor chip, the protective layer comprisingnanoscale particles, wherein the semiconductor chip with protectivelayer has been formed by the method of claim
 1. 4. The method of claim1, wherein the entire surface of at least one side of each of thesemiconductor chips is coated with the sol.
 5. The method of claim 1,wherein the coating of the semiconductor chips with the sol is achievedby immersion of the semiconductor chips in the sol.
 6. The method ofclaim 1, wherein the coating of the semiconductor chips with the sol isachieved by spin coating the sol on at least one surface of thesemiconductor chips.
 7. The method of claim 1, wherein the protectivelayer formed on each of the semiconductor chips comprises ascratch-resistant coating.
 8. A method for coating semiconductor chipswith nanoscale particles, comprising: hydrolyzing at least one ofsilanes and alkoxides to form a hydrolyzed material; preparing a solwith the hydrolyzed material; coating semiconductor chips with the sol;forming a gel layer or green layer from the sol by at least one of agingand drying the semiconductor chips coated with the sol; and forming aprotective layer on the semiconductor chips by sintering thesemiconductor chips coated with the gel layer or green layer.
 9. Themethod of claim 8, wherein sintering additives are added to reduce thesintering temperature required to form the protective layer.
 10. Asemiconductor chip including a protective layer coating at least aportion of the semiconductor chip, the protective layer comprisingnanoscale particles, wherein the semiconductor chip with protectivelayer has been formed by the method of claim
 8. 11. The method of claim8, wherein the entire surface at least one side of each of thesemiconductor chips is coated with the sol.
 12. The method of claim 8,wherein the coating of the semiconductor chips with the sol is achievedby immersion of the semiconductor chips in the sol.
 13. The method ofclaim 8, wherein the coating of the semiconductor chips with the sol isachieved by spin coating the sol on at least one surface of thesemiconductor chips.
 14. The method of claim 8, wherein the protectivelayer formed on each of the semiconductor chips comprises ascratch-resistant coating.